Wireless sensor systems that employ resonant circuit technology are known. These systems may utilize a passive wireless sensor in remote communication with excitation and reader circuitry. Often the wireless sensor is implanted at a specific location, such as within the human body, to detect and report a sensed parameter. In some systems, the sensed parameter varies the resonant frequency of the wireless sensor. A reader device may detect the resonant frequency of the wireless sensor to determine the sensed parameter.
Wireless sensor systems may generally include a reader unit or device that may be configured to be placed in a use condition for taking readings from the sensor and in a resting condition in which it is not communicating with the sensor. For example, a reader unit may be handheld or battery operated and be adapted for use a few minutes each day. This reader unit may also be configured to sit on a recharging (“docking”) station during times of non-use. Sensor/reader systems may incorporate many types of wireless technology: active & passive sensors, continuous wave (CW) & modulated data transmission, and analog & digital type systems.
In one application, passive wireless sensor systems may employ resonant circuit technology. Passive wireless sensor systems may be pressure monitoring devices for use by themselves or incorporated into other medical devices including, without limitation, pacemakers, defibrillators, drug elution devices, or ventricular assist devices (VADs). In one embodiment, a medical device includes one or more sensors that are configured to be positioned at a desired location within the human body. The sensor may be fabricated using microelectromechanical systems (MEMS) technology and may be configured to transmit wireless data to an external receiver/reader to facilitate transmission of diagnostic health data to a physician, clinician, a nurse, a patient's caregiver, or the patient.
One such sensor formed using a MEMS technique has an inductive and capacitive nature. The sensor comprises an inductor (L) and a capacitor (C) connected together in parallel, commonly called an LC tank circuit. The geometry of the sensor allows for the deformation of a capacitive plate with increased pressure. This deformation leads to a deflection of the plate and hence a change in the capacitance value of the system. The LC tank circuit also generates an electronic resonating frequency. This resonating frequency is related to the inductive and capacitance values of the circuit and will change with the deflection of capacitor plates under changing pressure. This emitted resonating frequency signal is received by an external wireless receiver/reader and deciphered into a correlative pressure reading.
Such sensors may also include wireless data transmission capability. The device may require no battery or internal power. Rather, the sensor may be powered by an inductively coupled electromagnetic (EM) field that is directed towards its inductor coil. The receiver/reader device may provide the electromagnetic field by generating a radio frequency (RF) burst or other signal. The inductor receives energy from the EM field to cause the sensor LC tank to resonate and store energy. When the external EM field is removed, the inductance and capacitance form a parallel resonant circuit to radiate energy through the inductor which acts as an antenna. This oscillating circuit will then produce RF signals, whose frequency is proportional to the capacitive value of the sensor, which varies with pressure. The inductor coil may serve both as an inductor creating the oscillating RF signals having a frequency proportional to the capacitance of the sensor at a certain pressure, and as an antenna coil emitting the RF signal generated by the LC tank circuitry.
In one embodiment, the pressure sensor may include an inductor/capacitor circuitry assembled in a parallel configuration. In other embodiments, it may include a piezoelectric, piezo-resistive or capacitive pressure sensor. In the inductor/capacitor circuitry, the resonant frequency of the energized circuit will change with the internal pressure of the patient. The sensor transmits sensed or detected pressure readings wirelessly to an external system receiver through RF signals without the requirements of an internal powering system. In a particular embodiment, the sensor may be energized through electromagnetic fields that are directed to a circuitry of the sensor.
Current designs for wireless sensor readers and related systems, such as those disclosed in commonly owned U.S. Pat. No. 8,154,389 filed on Apr. 7, 2009, U.S. Pat. No. 8,432,265 filed on Mar. 19, 2012, U.S. Pat. No. 8,493,187 filed on Mar. 19, 2010, and U.S. Pat. No. 8,570,186 filed on Apr. 25, 2012, U.S. Pat. No. 9,867,552 filed on Jun. 29, 2012, U.S. Pat. No. 9,305,456 filed on Apr. 9, 2013, U.S. Pat. No. 9,489,831 filed on Sep. 30, 2013, U.S. Pat. No. 9,721,463 filed on Mar. 29, 2016, U.S. Pat. No. 9,894,425 filed on Nov. 7, 2016 are incorporated by reference herein. These patents disclose systems configured to communicate wirelessly with a sensor at a remote location and obtain a reading.
Wireless sensor readers intended for frequent use by medical patients at home are particularly useful for taking measurements of internal body parameters of interest to caregivers. In order to ensure patient compliance in taking these readings, consistently, and correctly, however, there is a need for improving the functionality of this system and in particular improving the functionality and usability of the reader. Further, there is a need to allow a user to easily incorporate the reader and associated system within their day to day lifestyle and for improving the reliability of the reader in the field, to ensure functionality, accuracy, and secure data management.